Polyethersulfone/polyester block copolymers and a process for their preparation

ABSTRACT

A block copolymer resin containing structural units conforming to ##STR1## and a method for its preparation are disclosed. Accordingly, the block copolymer is prepared by reactive blending of an ester-containing polyether sulfone with a polyester. The block copolymer resin thus produced is characterized by its homogeneous morphology. The high level of its mechanical properties makes the resin suitable for a variety of applications.

This application is a division of application Ser. No. 08/311,621 filedSep. 23, 1994, Now U.S. Pat. No. 5,500,479.

FIELD OF THE INVENTION

The invention relates to a process for preparing block copolymers andmore particularly to reactive blending of ester-containing polyethersulfones with a polyester.

BACKGROUND OF THE INVENTION

Polyesters are well-known commercially available resinous materialswhich are high temperature, high performance thermoplastic engineeringpolymers with a combination of good thermal and good mechanicalproperties. These resins which are typically prepared by thecondensation reaction of dihydroxy compounds and aromatic dicarboxylicacids are suitable in a variety of applications.

The art has long recognized the advantages of modifying the propertiesof resinous polymers by copolymedzation techniques. In this regard, thepreparation of block copolymers based on polyether/polyester carbonatehas been disclosed in U.S. Pat. No. 5,169,907. In the process thusdisclosed a polyether ketone (or other polyaryl ether)/polycarbonateblock copolymer is prepared by transesterification of an estercontaining polyaryl ether and a polycarbonate. Also relevant is U.S.Pat. No. 4,517,354 which disclosed certain polysulfone which may uponreacting with polyols or with polyamines yield the correspondingpolyesters or polyamides. Blends of a poly(aryl ether), a polyalkyleneterephthalate and a nucleating agent have been disclosed in U.S. Pat.No. 4,906,500. Blends of polyether sulfone with polyalkyleneterephthalate have been disclosed in U.S. Pat. No. 5, 151,462. Alsorelevant is European Patent Application 133,907, which disclosed a blendof polyarylether sulfone with a thermoplastic polyester. Polyarylateshaving improved hydrolytic stability were disclosed in U.S. Pat. No.5,036,150. The arylates have repeating units derived frombis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone optionally a dihydric phenoland a mixture of isophthalic acid and terephthalic acid or theirderivatives.

It is an object of the present invention to provide block copolymers ofpolyethersulfone/polyester which have a predictable block length.

It is another object of the present invention to providepolyethersulfone sulfone/polyester block copolymers which may be formedin an extruder.

It is also an object of the present invention to provide a process forproducing polyethersulfone sulfone/polyester block copolymer viareactive melt blending.

Another object of the present invention to provide a process forproducing polyethersulfone sulfone/polyester block copolymers which maybe carried out in a relatively short period of time.

These and other objects which will be apparent to those skilled in theart are accomplished by copolymerizing an ester group containingpolyethersulfone (herein ePSU) with a thermoplastic polyester. Thiscopolymerization is carried out, with or without a catalyst, by reactivemelt blending of the components.

SUMMARY OF THE INVENTION

A block copolymer resin conforming structurally to ##STR2## and a methodfor its preparation are disclosed. Accordingly, the block copolymer isprepared by reactive blending of ePSU with a polyester. The blockcopolymer resin thus produced is characterized by its level ofhomogeneity on a microscopic scale. The high level of its mechanicalproperties makes the resin suitable for a variety of applications.

DESCRIPTION OF THE FIGURES

FIG. 1 is an electron micrograph (magnification of 7500:1) of thestructure of a blend of PET and polyether sulfone (PSU).

FIG. 2 is an electron micrograph (magnification of 7500:1) of thestructure of the copolymer of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to block copolymers containing structuralunits conforming to ##STR3## in which A and Z independently one of theother denote the residue of a

C₆ -C₂₄ aromatic dicarboxylic add,

B is the residue of an aliphatic or cycloaliphatic C₂ -C₈ diol,

E₂ denotes the residue of a dihalodiaryl sulfone and

E₁ denotes the residue of a aromatic dihydroxy compound, and

n is an integer of 1 to 100 preferably about 5 to 20, and

m is an integer of 1 to 100, preferably 5 to 20.

The term "residue" as used in the context of this invention refers tothat portion of the compound without its reactive functional groups.

The block copolymer of the invention is prepared by reactive blending inthe melt. The reactants comprise

(i) ePSU containing structural units conforming to ##STR4## and (ii) athermoplastic polyester containing structural units conforming to##STR5## where the terms have the meaning noted above.

The relative molar amounts of these reactants are 10 to 90% of ePSU and10 to 90% of thermoplastic polyester. The preferred ranges are 30 to 70%of ePSU and 30 to 70% of thermoplastic polyester. The reaction inaccordance with the present invention is carded out by melt blending attemperatures above about 250° C., typically in the presence of a Lewisadd as catalyst, for a period not less than 0.5 minutes, more typically2 to 30 minutes, to produce the inventive block copolymer.

A process for the preparation of an ester group-containing polyethersulfone has been disclosed in patent application Ser. No. 081010,736which was filed Jan. 29, 1993 (Attorney Docket Number Mo3903) and whichshares a common assignee with the instant application. Essentially, ePSUmay be prepared by reacting a dihalogenodiphenyl sulfone with excessamount of an aromatic dihydroxy compound to form a reaction product, andthen reacting a carboxylic add or its derivative with the reactionproduct to produce an ester group-containing polyether sulfone. Thecarboxylic acid derivative in the present context is any of dicarboxylicadd halide or the anhydride of such adds, for instance an acid chlorideor its anhydride. The amount of dicarboxylic acid halide used is thatwhich is sufficient to react with the excess amount of the aromaticdihydroxy compound and with said reaction product.

The dihalogenodiphenyl sulfone suitable in the process of the inventionconforms to

    X--Ar--SO.sub.2 --Ar--X

wherein X denotes a halogen preferably F, Cl or Br, and Ar denotes C₆-C₂₄ aryl, alkylaryl or cycloalkylaryl. The preferred dihalogenodiphenylsulfone is 4,4'-dichlorodiphenyl sulfone.

The aromatic dihydroxy compound conforms to formulae (1) or (2).##STR6## wherein A denotes an alkylene group with 1 to 8 carbon atoms,an alkylidene group with 2 to 8 carbon atoms, a cycloalkylene or acycloalkane group with 5 to 15 carbon atoms, a cycloalkylidene groupwith 5 to 15 carbon atoms, a carbonyl group, an oxygen atom, a sulfuratom, --SO--or--SO₂ -or a radical conforming to ##STR7## g denotes thenumber 0 to 1; Z denotes F, Cl, Br or C₁ -C₄ -alkyl and if several Zradicals are substituents in one aryl radical, they may be identical ordifferent from one another;

d denotes an integer of from 0 to 4; and

f denotes an integer of from 0 to 3.

Among the dihydroxy compounds useful in the practice of the inventionare hydroquinone, resorcinol, bis-(hydroxyphenyl)-alkanes,bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones,bis-(hydroxyphenyl)-sulfides, bis-(hydroxyphenyl)-sulfones, andα,α-bis-(hydroxyphenyl)-diisopropyl-benzenes, as well as theirnuclear-alkylated compounds. These and further suitable aromaticdihydroxy compounds are described, for example, in U.S. Pat. Nos.3,028,356; 2,999,835; 3,148,172; 2,991,273; 3,271,367; and 2,999,846,all incorporated herein by reference. Further examples of suitablebisphenols are 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A),2,4-bis-(4-hydroxyphenyl)-2-methyl-butane,1,1-bis-(4-hydroxyphenyl)-cyclo-hexane,4,4'-(3,3,5-trimethyl-cyclohexylidene)diphenol,α,α'-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,2,2-bis-(3-methyl-4-hydroxyphenyl)-propane,2,2-bis-(3-chloro-4-hydroxyphenyl)-propane,bis-(3,5-dimethyl-4-hydroxyphenyl)-methane,2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,-bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfide,bis-(3,5-dimethyl-4-hydroxy-phenyl)-sulfoxide,bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane, α,α'-bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropyl-benzene and 4,4'-sulfonyldiphenol.

Examples of particularly preferred aromatic bisphenols are 2,2-bis-(4-hydroxyphenyl)-propane,2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane and1,1-bis-(4-hydroxyphenyl)-cyclohexane.

The most preferred bisphenol is 2,2-bis-(4-hydroxyphenyl)-propane(bisphenol A).

The carboxylic acid derivative is preferably an aromatic carboxylic addhalide preferably conforming to

    Hal--C(O)--Ar--C(O)--Hal

where Ar is an aromatic radical, most preferably terephthaloyl chlorideor isophthaloyl chloride.

In preparing ePSU, the relative molar amounts of the reactants may rangeas follows: aromatic dihydroxy compound: dihalogenodiphenyl sulfone:carboxylic acid derivative=3:2:1 to 21:19:2.

The first step of the process for preparing ePSU is carried out in asolvent or a mixture of solvents and in the presence of a base. Thesolvent is an aprotic polar solvent or its mixture with a second solventwhich will form an azeotrope with water. The preparation of ePSU isgenerally carried out in the presence of a basic catalyst. The base,used at an equivalent ratio ≧1 is an alkali, or alkaline earth, metalhydroxide or the corresponding carbonate. Examples include potassiumcarbonate, potassium hydroxide, sodium carbonate, sodium bicarbonate andcalcium hydroxide.

Suitable solvents include N-methylpyrrolidone, N-methyl-caprolactam,dimethylsulfoxide, diphenylsulfone and sulfolan. These solvents aregenerally employed in an amount of from about 0.5 to about 50 parts byweight, preferably from about 2 to about 20 parts by weight based on thetotal weight of the reactants.

The ePSU is generally prepared by reacting the dihalide and bisphenolsat temperatures of from about 130 to about 320° C. for from about 1 toabout 50 hours. Suitable techniques for carrying out the reaction forpreparing ePSU are known.

The ePSU suitable for the preparation of the block copolymer of thepresent invention has a number average molecular weights (as determinedby gel permeation chromatography using polystyrene as the standard) offrom about 560 to about 300,000, preferably from about 1000 to about200,000 and most preferably from about 2000 to about 100,000.

In the process in accordance with the present invention, ePSU is reactedwith a thermoplastic polyester under conditions of reactive meltblending. The thermoplastic polyesters useful in the context of theinvention are preferably poly(alkylene terephthalates) selected from thegroup consisting of poly(ethylene terephthalate), poly(butyleneterephthalate) and poly(alkylene naphthalates). The polyesters have anintrinsic viscosity of about 0.4 to 2.0 dl/g as measured in a 60:40phenol/tetrachloroethane mixture or similar solvent at about 23 to 30°C.

Specific examples of appropriate polyesters include those containingstructural units conforming to ##STR8## in which B represents theresidue of a C₂ -C₈ aliphatic or cycloaliphatic diol, preferably C₂ -C₄aliphatic diol and A denotes the residue of a C₆ -C₂₄, preferably C₆-C₁₀ aromatic dicarboxylic acid.

The suitable thermoplastic polyesters also include copolyesters based ontwo or more of the suitable acids or diols. The suitable polyesters areknown and are readily available in commerce. Alternatively, suitablepolyesters may be made by following the teachings of for example U.S.Pat. Nos. 2,465,319, 2,901,466 and 3,047,539 which are incorporatedherein by reference.

A catalyst is not necessary in the process of the present invention,however, it would be possible to include a catalyst. Where used, thecatalyst is generally employed in an amount of from about 0.1 to about1.0 wt. %. Spedtic examples of suitable catalysts include: potassiumacetate, sodium acetate, antimony trioxide.

The process of the present invention may carded out at temperatures offrom about 250° C. to about 400° C. preferably, from about 300° C. toabout 350° C. in conventional kneaders or extruders provided the timeand temperature conditions which are required in accordance with theinvention are adhered to.

Morphologically, the block copolymers of the present invention arehomogeneous. They feature good mechanical properties at hightemperatures.

Having thus described our invention in detail, the following examplesare given as being illustrative thereof. All parts and percentages givenin these examples are parts by weight and percentages by weight, unlessotherwise indicated.

EXAMPLES Example 1 Synthesis of Ester-containing Poly (ethersulfone)

Difluorodiphenylsulfone (25.43 g; 0.1 mol), bisphenol A (18.7 g; 0.082mol), 4'-hydroxy phenyl-4-hydroxybenzoate (4.14 g; 0.018 mol), and K₂CO₃ (15.2 g; 0.11 mol) were combined with 100 ml of NMP and 65 mltoluene in a 250 ml 3-neck flask (all glassware was previously flamedried). A mechanical stirrer, Dean-Stark trap (12 ml volume) withcondenser and N₂ outlet and a Claisen adapter with N₂ inlet andthermocouple were attached and the entire system was purged with N=for10 minutes. The solution was heated at 155° C. for 8 hours. During thistime, toluene and water collected in the Dean-Stark trap. After 8 hours,20 ml of toluene and water were allowed to drain from the trap and thetemperature was raised to 180° C. After 5 hours, the toluene was drainedand the temperature increased to 187° C. for 2 hours. During this time,the yellow/green solution became very viscous. The solution was cooledto room temperature, diluted with 100 ml NMP and then poured into alarge excess of methanol to precipitate a fibrous white polymer. Thefibrous white polymer was collected and redissolved in methylenechloride. The methylene chloride solution was washed with 10% HCl andwater and then poured into methanol to precipitate the polymer. Thepolymer was dried in vacuum at 80° C. for 8 hours. A yield of 97% -99%was achieved.

The resulting polymer was characterized as follows: Molecular weight asmeasured by GPC (polystyrene standard) M_(w) =55600; M_(n) =25600; M_(w)/M_(n) =2.2. Thermal properties as measured by DSC: T_(g) =154°C.

Example 2. Synthesis of Ester-containing Poly (ethersulfone)

Difluorodiphenylsulfone (25.43 g; 0.1 mol), bisphenol A (20.75 g; 0.0909mol), 4-hydroxy phenyl-4-hydroxybenzoate (2.093 g; 0.0091 mol.), and K₂CO₃ (15.2 g; 0.11 mol) were combined with 100 ml of NMP and 65 mltoluene in a 250 ml 3-neck flask (all glassware was previously flamedried). A mechanical stirrer, Dean-Stark trap (12 mL volume) withcondenser and N₂ outlet and a Claisen adapter with N₂ inlet andthermocouple were attached and the entire system was purged with N₂ for10 minutes. The solution was heated at 155° C. for 8 hours. During thistime, toluene and water collected in the Dean-Stark trap. After 8 hours,20 ml of toluene and water were allowed to drain from the trap and thetemperature was raised to 180° C. After 5 hours, the toluene was drainedand the temperature increased to 187° C. for 2 hours. During this time,the yellow/green solution became very viscous. The solution was cooledto room temperature, diluted with 100 ml NMP and then poured into alarge excess of methanol to precipitate a fibrous white polymer. Thisfibrous white polymer was collected and redissolved in methylenechloride. The methylene chloride solution was washed with 10% HCl andwater and then poured into methanol to precipitate the polymer. Thepolymer was then dried in a vacuum at 80° C. for 8 hours. A yield of 97%-99% polymer with an inherent viscosity (NMP, 30° C.) of 0.45 dl/g wasobtained. Thermal properties as measured by DSC: T_(g) =165° C.

Example 3

A 500 ml 3-neck flask was loaded with dichlorophenyl sulfone (29.4 g;0.102 mol), bisphenol-A (28.5 g; 0.125 mol), K₂ CO₃ (19.7 g; 0.14 mol),200 ml of N-methyl pyrrolidone and 60 ml of toluene. The reaction flaskwas fitted with a Dean-Stark trap and mechanical stirrer and was heatedto 155° C. The reaction mixture was left stirring at 155° C. for about 6hours, collecting H₂ O in the trap. The reaction mixture wassubsequently heated to 180° C. for 6 hours while distilling off thenecessary amount of toluene. After allowing the reaction mixture tocool, terephthaloyl chloride (4.7 g, 0.02 mol) and triethylamine (10 ml)were added. The reaction mixture was subsequently precipitated intomethanol, re-dissolved in methylene chloride, washed three times with 50ml of 1N HCl, and three times with distilled water and precipitated intomethanol. The structure was conforms to ##STR9## was verified by IR,specifically to the carbonyl band at 1725 cm⁻¹. The molecular weight(M_(n)) of the product was 26,000. The ePSU of this example containsabout 20 mol % ester groups.

Example 4

Preparation of Block Copolymer in a Haake Mixer: The ester-containingpolyethersulfone prepared in accordance with Example 3 and thermoplasticpolyester (PET) which is sold under the trademark Ektar by Eastman Kodakat a weight ratio between them of about 53/47 were placed in a Haakemixer equipped with kneading elements. The polymers were melt blended at340° C. for 40 min. The product thus prepared was then used for thepreparation of test specimens by hot-pressing at 340° C. for 2 minutesunder a pressure of 2 MPa. Films of the as-kneaded sample of blockcopolymers were viewed by transmission electron microscopy (RuO₄stained). A comparison was conducted by blending corresponding amountsof PET with PSU which contained no ester groups.

FIG. 1 is an electron micrograph (magnification of 7500:1) of thestructure of a blend of PET and PSU. FIG. 2 is an electron micrograph(magnification of 7500:1) of the structure of a reactive blend of PETand ePSU. These micrographs demonstrate the advantage represented by thereactive blending of the present invention over the mere blending ofclosely corresponding components. The former is much more homogeneousthan the later.

Example 5

The table below summarizes the results of the evaluation of a blend ofPETIPSU set in comparison to the block copolymer of the invention. Theblock copolymer exhibits a single glass transition temperature. Theblock copolymer also has a lower degree of crystallinity as evidenced byits lower melt temperature (T_(m)) and enthalpy of melting (ΔH).

    ______________________________________                                                Blend        Block Copolymer                                          ______________________________________                                        T9        68 and 168° C.                                                                        168° C.                                       Tm        240° C. 195° C.                                       ΔH  23.5 J/g       6.7 J/g                                              ______________________________________                                    

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A block copolymer containing structural unitsconforming to ##STR10## in which A and Z independently one of the otherdenote the residue of a C₆ -C₂₄ aromatic dicarboxylic acid,B is theresidue of an aliphatic or cycloaliphatic C₂ -C₈ diol, E₂ denotes theresidue of a dihalodiaryl sulfone and E₁ denotes the residue of aaromatic dihydroxy compound, and n and m, independently are integers ofabout 1 to
 100. 2. The copolymer of claim 1 wherein said A and Zindependently denote a C₆₋₁₀ aromatic dicarboxylic acid.
 3. Thecopolymer of claim 1 wherein said m and n independently denote 5 to 20.